Windblown snow, dust and sand can create hazardous driving conditions by reducing visibility and forming drifts on roadways to block or impede traffic movement. Blowing snow also causes icy roads, which are a major cause of vehicle accidents. Blowing snow can create significant problems on railroads by forming drifts that block the passage of trains where tracks pass through cuts in hills, and by clogging switches and interfering with the operation of electronic sensors for detecting over-heated journals and dragging equipment. There are many other well-known problems associated with blowing and drifting snow, dust, sand and other windblown particles.
Snow control devices in the form of snow fences and other structures have been used for many years to alleviate the problems created by blowing and drifting snow. The typical construction of a snow fence is a two-dimensional panel with a series of slots, holes or openings formed through the panel to create porosity. The snow fence creates aerodynamic drag and alters the structure of the turbulence which slows the velocity of the wind and diminishes its capacity to carry snow. In addition, a porous snow fence reduces the scale of turbulence by breaking up large eddy currents into smaller ones, thereby reducing the entrainment of particles. These effects on the wind allow the transported windblown particles to settle out and accumulate in a protected area which is sheltered by the snow fence. In the case of a porous snow fence, most of the snow deposition occurs in the protected area of the snow fence. Immediately downwind beyond the protected area is a critical area where the wind carries very little snow, because the substantial majority of the snow has been removed as the wind passes through the protected area. By positioning the snow fence far enough away from the roadway, railroad tracks or other object or area where snow accumulation is to be avoided, the snow settles out of the wind in the protected area before reaching the critical area. The wind is relatively free of snow within the critical area, so snow does not accumulate to a significant degree within the critical area which encompasses the roadway, railroad tracks or other object. Because the wind will pick up and saltate additional snow particles by blowing over expanses of snow-covered ground, the snow fence and its protected area must be close enough to encompass the roadway, railroad tracks or other object within the critical area to prevent the wind from accumulating snow again before reaching the roadway, railroad tracks or other object. Otherwise, the placement of the snow fence will be ineffective in preventing snow accumulation in the area where snow accumulation is to be avoided.
Typically, the panels of a snow fence are assembled in long continuous rows. Long rows of panels are usually necessary to achieve the best windblown particle control effects over relatively long expanses of critical areas such as roadways and railroad tracks. The panels are typically constructed of wood planks and/or steel or plastic sheeting. Posts or triangular support frame structures anchor the panels to the ground and hold them upright to confront and withstand the forces from the wind. Because of their relative massive, complex and sturdy nature, conventional snow fences are usually built in place as permanent installations. The nature of the materials used to construct such snow fences usually makes their fabrication a time-consuming exercise. In addition to being bulky, the construction materials are usually expensive and difficult to transport to the construction site. The typical end result of constructing such snow fences is a collection of immobile, expensive and artificial structures which are visually obtrusive and aesthetically objectionable in a natural environment.
While it is theoretically possible to remove the snow fences during the seasons or parts of the year when they are not needed, and thereby avoid the objectionable environmental obtrusion during at least some parts of the year, the cost of dismantling a typical snow fence and reassembling the snow fence when or where it is needed becomes a predominant deterrent, resulting in the snow fence remaining in place on a year-around basis. The same considerations apply with respect to moving those snow fences which have not been placed in an optimal position to prevent snow from drifting and accumulating in areas where snow accumulation is not wanted. Empirical experience may be required to obtain the optimal placement of a snow fence.
The cost of dismantling a snow fence is approximately the same as the considerable cost of fabricating the snow fence in the first place. Then, the dismantled snow fence must be reconstructed, again at a further cost approximately equal to the original fabrication cost. The time required to dismantle a snow fence may be slightly less than the time required to fabricate the snow fence in the first instance, but the time requirements are considerable and significant. The relatively permanent posts and anchoring structures used to hold the snow fence panels to the ground can not be removed, even though the panels might be removed from those posts and anchoring structures.
Even ignoring the substantial expense and time required to disassemble a conventional snow fence, the relatively large amount of construction materials from which the snow fence is fabricated must be stored until the time when the snow fence is again reassembled. The amount of material and the transportation costs of those materials between the site of use and the storage location create additional problems and difficulties. The amount of space required to store the construction materials of a typical wooden panel snow fence is substantial. Use of that space for storage constitutes an additional cost associated with disassembling a snow fence, which further deters dismantling the conventional snow fence during those times when it is not needed.
Because of the negative impacts of the cost, obtrusiveness, fabrication, dismantlement, removal and storage issues described above, previous artificial snow fences and windblown particle control structures have not been used on a prevalent basis for other beneficial purposes, such as accumulating snow in agricultural fields to increase the soil moisture content for growing crops, retaining the topsoil against wind erosion, or shielding immature plants from the shear stress of wind and from the rapid evaporation of soil moisture at their critical early-growth stages. These and other potentially beneficial uses of windblown particle control devices would become more prevalent, if the costs of such control devices since its were reduced to enable their cost-effective use over large expanses of agricultural fields, if such control devices could be fabricated and dismantled conveniently and efficiently, and if such control devices could be stored efficiently when not in use. Removing such control devices from agricultural fields is essential after stable plant growth has been established to permit tending to and harvesting of the crops, among other things. Many of the same considerations are also applicable to other uses of windblown particle control devices, including keeping roadways and railroad tracks clear of snow and ice.
Apart from controlling windblown particles, various silt and sediment control devices and artificial reef structures have been devised to deposit and control silt, sediment and other waterborne particles in moving bodies of water. The fluid dynamic drag and turbulence effects necessary to control waterborne particles are considerably different from those necessary to control windblown particles. For example, fluid dynamic effects are related to the density of the medium, to the density of the transported particles, and to the square or cube of the flow velocity. The density of water is approximately 1000 times that of air and the velocity of wind is typically 10–50 times the speed of moving water. The magnitudes of difference in the fluid dynamic effects imply that waterborne particle control devices and windblown particle control devices are not readily interchangeable for performing the same tasks.
The expense and construction of silt, sediment and waterborne particle control devices also make them unsuitable for use in controlling windblown particles. Silt and sediment control devices must be constructed of relatively high strength steel members that are bolted or welded together, since such waterborne control devices must be capable of withstanding the considerable force of the higher density moving water and impacts from large objects that might be carried in the water. The structures are then reinforced and held in place by steel cables. Bolting or welding steel members together is time consuming and relatively expensive. Disassembling waterborne particle control devices is not contemplated because they are intended for continual use. Placing waterborne particle control devices in flowing rivers and along beaches is a difficult task and typically requires heavy equipment such as cranes and barges to transport and position the devices permanently in place.
Many other disadvantages and use considerations are associated with conventional snow fences and windblown and waterborne particle control devices. These disadvantages and considerations have led to the improvements of the present invention.